Wafer transfer device

ABSTRACT

A wafer transfer apparatus for taking out a wafer from a wafer cassette having grooves on both ends for holding circumferential edges of a plurality of wafers by moving a wafer transfer arm in height directions and back and forth directions relative to the wafer cassette. The apparatus comprises a wafer pushing out mechanism for pushing out a wafer on the back of a wafer inlet/outlet side of the wafer cassette into which the transfer arm is inserted. The wafer pushing out mechanism comprises a pushing pin rotatable when it is in contact with the wafer and a driving mechanism for driving the pushing pin so as to push the wafer from the back of the wafer cassette to the wafer inlet/outlet side.

TECHNICAL FIELD

The present invention relates to a wafer transfer apparatus for takingout a wafer from a wafer cassette and transfer it to another apparatus,if necessary, in order to inspect it or subject it to a subsequentprocess.

BACKGROUND ART

FIG. 8 shows an example of conventional wafer transfer apparatuses fortaking out a wafer from a wafer cassette by means of a transfer arm.More specifically, a wafer cassette 4 storing a number of wafers 3 ismounted on a cassette base 2 movable up and down by an elevatormechanism portion 1, such that a wafer-inlet/outlet side faces atransfer arm 5 having an attracting portion 6. The transfer arm 5 has ageneral structure movable forward and backward relative to the wafercassette 4.

An operation of the conventional wafer transfer apparatus will bedescribed in brief. First, the cassette base 2 is moved down by theelevator mechanism portion 1, and the number of detected wafers iscounted by sensors (not shown), thereby detecting a wafer 3 to betransferred. After the sensor detects the wafer 3, the cassette base 2is moved up by a predetermined amount, and the transfer arm 5 is movedtoward the wafer cassette 4 and inserted under the wafer 3 to betransferred. After the transfer arm 5 is inserted, the cassette base 2is moved down by a predetermined amount by means of the elevatormechanism portion 1, so that the wafer to be transferred is placed onthe transfer arm 5. Then, the wafer 3 to be transferred is attracted bythe attracting portion 6, the transfer arm 5 is drawn out of the wafercassette 4, and the wafer 3 to be transferred is extracted andtransferred to a next step, such as an inspecting step.

In the wafer transfer apparatus described above, a plurality of slotgrooves 7, for holding the wafers 3 horizontally, are formed in bothside walls in the wafer cassette 4 for storing the wafers 3. A viewencircled in a right portion of FIG. 8 is an enlarged view showing slotgrooves 7 in the right side wall of the wafer cassette 4 viewed from thewafer 3-inlet/outlet side. As shown in the drawing, the cross section ofa slot groove is a tapered trapezoid, so that the area in which acircumferential edge portion of the wafer 3 contacts to the groove canbe as small as possible, to reduce the friction between the groove 7 andthe wafer 3, keep the wafer 3 horizontally and make it easy to take inand out the wafer 3.

FIG. 9 is a cross sectional view of the wafer cassette 4 storing thewafers 3, taken along a line between slots and viewed from a positionabove the apparatus. The top side of FIG. 9 corresponds to thewafer-inlet/outlet side. The dot line represents a walls connectingmember provided on a bottom portion of the cassette 4.

As shown in FIG. 9, the cassette 4 has a trapezoidal shape, the width ofwhich decreases toward the back side, for the purpose of preventing thewafer 3 from dropping down, when the disk-shaped wafer 3 is stored ineach slot groove 7. More specifically, a back-side opening 8, whichopens in the back side of the wafer cassette 4 (the bottom side of FIG.9), is narrower than the diameter of the wafer 3, so that the wafer 3 isbrought into contact with back-around portions 701. Thus, the wafer isprevented from dropping down from the back side of the wafer cassette 4.

Recently, the wafers have become thinner with the improvement of thetechnique of polishing the wafers 3 and by the request of the users. Forexample, a standard thickness of a conventional wafer 3 was about 0.6mm, whereas a recent wafer can be polished to a thickness of about 0.1mm. As the wafer 3 is thinned, a back circumferential edge portion ofthe wafer 3 is wedged into the back-around portions 701 of the wafercassette 4.

The wedged state of the circumferential edge portion of the wafer 3 intothe back-around portions 701 poses the following problems.

(1) When the wafer 3 is moved up by the transfer arm 5, in the statewhere the back edge portion of the wafer 3 is wedged into theback-around portions 701, the wafer 3 is bent by force, resulting indamage of the wafer.

(2) When the back circumferential edge portion of the wafer 3 is wedgedinto the back-around portions 701, the wafer 3 is frequently stored witha forward or backward inclination. Therefore, it is possible that aspace is left between the transfer arm 5 and the wafer 3, resulting inan error in attraction by the attracting portion 6.

(3) The wafer cassette 4 storing wafers 3 is transferred betweendifferent steps and factories with the wafer-inlet/outlet side facingup. Therefore, the back circumferential edge portion of the wafer 3 mayprobably be wedged into the back-around portions 701 due to its ownweight.

When the wafers are transferred by a truck or an airplane, they aremoved by a transport cassette having a narrower slot width, inconsideration of instability during transportation, such as vibration.When they are replaced from the transport cassette to a transfercassette by the transfer arm or the transport cassette is used as atransfer cassette without replacement, it is highly possible that theback circumferential edge portion of the wafer 3 is wedged into theback-around portions 701 and the wafer 3 is stored with a forward orbackward inclination. When the wafer 3 which is not held horizontally isto be transferred by the transfer arm, since the distance between wafersis narrow, the transfer arm 5 easily interferes with the wafer 3. Inaddition, an attraction error may be caused.

On the other hand, in a case where the wafers are replaced from thetransport cassette to a transfer cassette, the engagement must bereleased manually to replace the wafers, which requires a troublesomeprocess.

DISCLOSURE OF INVENTION

The present invention was made in consideration of the above situations,and its object is to provide a wafer transfer apparatus which canrelease the engagement of a wafer with a slot groove, thereby surelypreventing the wafer from being damaged during transfer of the wafer,and preventing an attraction error due to the engagement.

The present invention provides a wafer transfer apparatus for taking outa wafer from a wafer cassette having grooves on both ends for holdingcircumferential edges of a plurality of wafers by moving a wafer takingout arm relative to the wafer cassette, the wafer transfer apparatuscomprising wafer pushing out means for pushing out a wafer engaged withthe groove of the wafer cassette, thereby releasing engagement. Thewafer pushing out means have engagement preventing means for preventinga wafer from engaging with a contact portion in contact with the wafer.

With this structure, the wafer is pushed out by the wafer pushing outmeans. Therefore, the engagement of the circumferential edge portion ofthe wafer with a groove of the wafer cassette can be released and thewafer can be hold horizontally with the grooves. As a result, when thewafer is taken out from the wafer cassette, damage of the wafer or anattraction error of the transfer arm can be prevented. Further, waferscan be smoothly moved from one wafer cassette to another, and a transferprocess can be performed even by a transport wafer cassette which has anarrow pitch width.

It is preferable that the engagement preventing means be a roller havinga rotatable contact portion in contact with the wafer.

Further, it is preferable that the wafer pushing out means comprisemoving means for pushing out the contact portion in contact with thewafer to the wafer inlet/outlet side of the wafer cassette and drivingmeans for linearly driving the moving means toward the wafer cassette.

With this structure, the engagement of the wafer with the groove of thewafer cassette is automatically released by driving the driving means,so that the wafer can be pushed out to the wafer inlet/outlet side.Therefore, if the wafer pushing out means is incorporated in the wafertransfer process, it is possible to perform wafer transfer free fromwafer damage or an attraction error of the transfer arm.

Furthermore, the wafer pushing out means may be characterized insimultaneously pushing out a plurality of wafers.

With this structure, it is also possible to release at a time theengagement of all wafers stored in the wafer cassette, resulting inimprovement of the efficiency of the transfer process.

Moreover, the wafer pushing out means may comprise moving means forpushing out the contact portion in contact with the wafer to the waferinlet/outlet side of the wafer cassette, and have a structure in whichthe moving means is manually driven linearly toward the wafer cassette,thereby simultaneously pushing out a plurality of wafers.

With this structure, the structure can be simplified and a low-costwafer transfer apparatus can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a structure of a wafer pushing mechanism during a pushingstandby time, used in a first embodiment;

FIG. 2 shows a structure of the wafer pushing mechanism during a pushingtime, used in the first embodiment;

FIGS. 3A and 3B show the wafer pushing mechanism used in the firstembodiment;

FIG. 3C shows a pushing pin used in the wafer pushing mechanism of thefirst embodiment;

FIG. 4 is a flowchart for explaining an operation of the firstembodiment;

FIG. 5 shows a second embodiment of the present invention;

FIG. 6 shows a third embodiment of the present invention;

FIG. 7 shows the back side of the third embodiment of the presentinvention;

FIG. 8. shows the overall structure of a conventional wafer transferapparatus; and

FIG. 9 shows the relationship between a slot groove and a wafer of aconventional wafer cassette.

BEST MODE OF CARRYING OUT THE INVENTION

First to third embodiments of the present invention will be describedwith reference to the accompanying drawings.

The basic structure of wafer transfer apparatuses of the first andsecond embodiments of the present invention is the same as thatdescribed above with reference to FIG. 8 except for a wafer pushingmechanism. Therefore, FIG. 8 is invoked.

First Embodiment

FIGS. 1 and 2 show a wafer transfer apparatus according to the firstembodiment of the present invention on a cross section similar to thatshown in FIG. 9. The wafer transfer apparatus has a wafer pushingmechanism 9, which faces a back-side opening 8 of a wafer cassette 4storing wafers 3. FIG. 1 shows a pushing standby time of the waferpushing mechanism 9, whereas FIG. 2 shows a pushing time of the waferpushing mechanism 9.

A general structure of the wafer pushing mechanism 9 will be describedfirst.

FIGS. 3A, 3B and 3C show a general structure of the wafer pushingmechanism 9 shown in FIGS. 1 and 2. FIG. 3A is an enlarged view of thewafer pushing mechanism 9 shown in FIG. 2, FIG. 3B is a side view ofFIG. 3A, and FIG. 3C is a cross sectional view of a pushing pin 907.

As shown in FIGS. 3A and 3B, the wafer pushing mechanism 9 comprises abase 901. Under the base 901, a motor 902 is provided. A rotation shaft9021 of the motor 902 protrudes above the base 901. A disk-shaped cam903 is eccentrically attached to the protruding rotation shaft 9021.

A sub-base 905 is attached to the base 901 via a linear movement guide904. The sub-base 905 is forced by a spring 9061 in a direction in whichit is attracted to the side of the base 901. A cam follower 906 isattached to the sub-base 905 so as to be kept in contact with thecircumferential edge of the diskshaped cam 903. When the disk-shaped cam903 is rotated by the motor 902, the sub-base 905 is moved linearly in adirection along the linear movement guide 904 against the attractiveforce of the spring 9061. The linear movement guide 904 is arranged toface the front of the back-side opening 8, such that the direction ofthe movement of the sub-base 905 along the linear guide 904 coincideswith the direction in which the wafer cassette 4 pushes the wafer 3.

Further, a plurality of (three, in the depicted example) push pins 907,908 and 909 are implanted in the sub-space 905 in a positionalrelationship such that they are in contact with the circumferential edgeof the wafer 3.

In the first embodiment, the implantation interval between the pushingpins 907 and 909 is wider than the orientation flat (hereinafterreferred to as the ori-fla) of the wafer 3. If the wafer is stored inthe cassette 4 such that the ori-fla of the wafer 3 is present betweenthe pushing pins 907 and 909, as will be described later, the twopushing pins push the wafer 3 out (the pin 908 does not contact to thewafer (ori-fla)). If the wafer is stored in the cassette 4 such that theori-fla is present in a portion other than the portion between thepushing pins 907 and 909, the three pushing pins 907, 908 and 908 pushthe wafer 3 along the arc of the wafer 3. Therefore, the wafer can bepushed by a constant amount regardless of the position of the ori-fla.

A general structure of the pushing pin 907 will be described next. Thepushing pins 908 and 909 also have completely the same structure.

As shown in FIG. 3C, a shaft 9072 is fixed to the is sub base 905 by afixing bolt 9071. A pushing pin body 9074, made of resin, is rotatablyattached to the shaft 9071 via bearings 9073. Since the pushing pin body9074 is rotatable when the wafer 3 is pressed by the pushing pin body9074, variable positions thereof are brought into contact with thecircumferential edge of the wafer 3, so that the circumferential edge ofthe wafer 3 cannot be wedged into the surface of the pushing pin body9074.

An operation of the first embodiment having the structure describedabove will be described with reference to FIG. 4.

FIG. 4 is a flowchart indicating a transfer operation of taking outwafers 3 from the wafer cassette 4 one by one and subjecting the waferto another process. In this case, the wafer 3 i-th from the lowermoststage (hereinafter referred to the i-th wafer 3) is taken out. Thecircumferential edge thereof is wedged into back-around portions 701 ofa slot groove 7. An operation of releasing the wedged state andtransferring the i-th wafer 3 by a transfer arm 5 will be described.When the wafer cassette 4 is mounted on a cassette base 2 which can bemoved up and down by an elevator mechanism portion 1, and a switch (notshown) is turned on to start transferring the wafer 3, an operation isperformed through the procedures shown in the flowchart.

In the following description, it is assumed that i=n, an n-th wafer 3 istransferred, and the ori-fla of the n-th wafer 3 is present between thepushing pins 907 and 909.

First, the cassette base 2 is moved down by the elevator mechanismportion 1 (step S401).

Then, a sensor (not shown) determines whether the n-th wafer 3 in thewafer cassette 4 is detected (step S402).

If the n-th wafer 3 is not detected in the step S402, the cassette base2 is further moved down by the elevator mechanism portion 1 (step S403),and the same operation is repeated until the n-th wafer is detected.

If the n-th wafer 3 is detected in the step S402, the cassette base 2 ismoved up by a predetermined amount U (step S404).

In this case, at a position where the wafer pushing mechanism 9 can pushout the n-th wafer 3, as shown in FIG. 1, the mechanism is set to astandby mode in which the pushing pins 907, 908 and 909 are separatedfrom the wafer 3 within a range of a stroke of the sub-base 905 so asnot to interfere with the n-th wafer 3. When the motor 902 is driven,the disk-shaped cam 903 eccentrically attached to the rotation shaft9021 is rotated. The rotation force is converted to force for pushingthe sub-base 905 by the contact between the disk-shaped cam 903 and thecam follower 906. Thus, the sub-base 905 is driven linearly toward thewafer inlet/outlet side of the wafer cassette 4 along the linear guide904 against the attractive force of the spring 9061. When the sub-base905 is driven linearly to the wafer inlet/outlet side, the pushing pins907 and 909 are pressed against the circumferential edge of the wafer 3,bridging the ori-fla 3A of the n-th wafer 3. At this time, the pushingpin 908 does not contact to the circumferential edge of the wafer 3, asshown in FIG. 2. The pushing pins 907 and 909 are then rotated, whilepushing the wafer 3, so that the engagement between the wafer 3 and theback-around portions 701 can be released (step S405).

The amount of pushing the wafer 3 by the pushing pins 907 and 909 can beadjusted by changing the size or the rotation angle of the disk-shapedcam 903. In this embodiment, an amount of a push of several millimetersis sufficient for the purpose of releasing the engagement.

Thereafter, when the disk-shaped cam 903 is further rotated by the motor902 while being in contact with the cam follower 906, the sub-base 905is moved along the linear guide 904 by the attractive force of thespring 9061 in a direction in which it is separated from the wafercassette 4. The pushing pins 907, 908 and 909 are returned to thestandby state as shown in FIG. 1 (step S406).

Then, the transfer arm 5 is inserted under the n-th wafer 3 (step S407),and the cassette base 2 is moved down by the elevator mechanism portion1 (step S408). After the transfer arm 5 attracts and holds the n-thwafer 3 by the attracting portion 6 (step S409), the transfer arm 5takes out the wafer 3 from the wafer cassette 4 (step S410).

The taken-out wafer 3 is transferred and subjected to various processesin accordance with the use, such as an inspection process (step S411).After the processes, the n-th wafer 3 is restored in the position fromwhich it is taken out by the transfer arm 5 (S412). In a state where theattraction of the wafer 3 is released, the cassette base 2 is moved upby the elevator mechanism portion 1 (step S413). The circumferentialedge portion of the n-th wafer 3 is held by the slot groove 7 and thetransfer arm 5 is moved to the standby position (step S414). Thus, theoperation of transferring the n-th wafer 3 is completed.

The same procedures as those described above are repeated with respectto all wafers 15 stored in the wafer cassette 4 (step S415), and thetransfer process is ended.

In the above description, it is assumed that the ori-fla of the wafer 3is present between the pushing pins 907 and 909. In contrast, if theori-fla is present outside the portion between the pushing pins 907 and909, all the pushing pins 907, 908 and 909 of the wafer pushingmechanism 9 are in contact with the circumferential edge portion of thewafer 3. If the ori-fla is present across either the pushing pin 907 or909, the pushing pin 908 and one of the pushing pins 907 and 909 are incontact with the circumferential edge portion of the wafer 3 to pressout the wafer.

With the wafer transfer apparatus described above, if the ori-fla of thewafer 3 is present between the pushing pins 907 and 909, the pushingpins 907 and 909 push out the circumferential edge portion of the wafer3 with rotating. Therefore, variable positions of the pushing pins arealways brought into contact with the circumferential edge of the wafer3, so that the engagement between the wafer 3 and the back-aroundportions 701 can be released without engagement between thecircumferential edge of the wafer 3 and the pushing pin body 9074(9094). In addition, the durability of the pushing pins 907, 908 and 909can be improved.

If the ori-fla of the wafer 3 is not present between the pushing pins907 and 909, at least two pushing pins including the pushing pins 908press out the circumferential edge portion of the wafer 3 with rotating.Therefore, the engagement between the wafer 3 and the back-aroundportions 701 can be released without engagement between thecircumferential edge of the wafer 3 and the pushing pin body 9074 (9084,9094).

Thus, wherever the ori-fla of the wafer 3 held by the slot groove 7 ispresent, the wafer can be pressed out by the same amount, thereby surelyreleasing the engagement. As a result, the transfer arm 5 can attracteach wafer 3 in the free state in which the engagement of the wafer 3with the wafer cassette 4 is released. Therefore, an attraction errorcan be prevented from occurring.

Further, since the pushing pins 907, 908 and 909 push the n-th wafer 3by driving the motor 902, the push by the pushing pins 907, 908 and 909can be controlled by controlling the drive of the motor 902. Therefore,it is easy to incorporate the pushing pins into the wafer transferapparatus, and a stable operation without damaging wafers can beautomated in the wafer transfer process.

The present invention is not limited to the first embodiment describedabove, but can be modified variously as described in the followingsections (1) and (2) without changing the gist of the invention.

(1) In the first embodiment, the engagement is released each time thewafer 3 stored in the wafer cassette is transferred. However, to improvethe throughput of the apparatus, the transfer process can be performedafter simultaneously releasing the engagement of a plurality or all ofthe wafers 3 stored in the wafer cassette 4. This modification can berealized easily by lengthening the pins.

(2) In the first embodiment, the cassette base 2 is moved up and down bythe elevator mechanism 1, without moving the transfer arm 5 up and down,to release the engagement and transfer each wafer 3 in the wafercassette 4. However, it is possible to employ a structure for releasingthe engagement and transferring each wafer by moving the pushingmechanism 9 and the transfer arm 5 up and down, instead of moving thecassette base 2 up and down.

Second Embodiment

In the structure of the first embodiment, wherever the ori-fla of then-th wafer 3 is present, the engagement between the circumferential edgeportion of the wafer 3 and the back-around portions 701 can be released.

However, the ori-flas of the wafers 3 stored in the wafer cassette 4 maybe aligned, depending on the process. Further, as in the case of an8-inch wafer, the wafer may have a notch, instead of an ori-fla.

As the second embodiment, a wafer transfer apparatus used only for thesecases will be described.

FIG. 5 is a schematic diagram showing a wafer transfer apparatusaccording to the second embodiment. The same elements as those shown inFIG. 1 are identified by the same reference numerals as those used inFIG. 1, and detailed descriptions thereof will be omitted.

In FIG. 5, a wafer pushing mechanism 9 faces a back-side opening 8 of awafer cassette 4 and comprises a pushing pin 910 implanted in a sub-base905. It is preferable that the diameter of the pushing pin 910 be muchlarger than the width of a notch in order to reduce the error in theamount of a push. In the same manner as in the first embodiment, when amotor 902 is driven, a disk-shaped cam 903 is rotated. The rotationcauses the sub-base 905 to be driven linearly via a cam follower 906,and a pushing pin body 9074 of the pushing pin 910 to be brought intocontact with the n-th wafer 3 with rotating. The sub-base pushes out thewafer 3, thereby releasing the engagement between the circumferentialedge portion of the n-th wafer 3 and back-around portions 701.

If the wafers 3 are stored in the wafer cassette 4 in a state where theori-flas face the back-side opening 8, when the wafer pushing mechanism9 is driven, the pushing pin 910 is brought into contact with theori-fla of the n-th wafer 3, releases the engagement of the wafer 3 andpushes the wafer to the position of the wafer 3′ represented by thedot-chain line. Thus, the pushed distance of the wafer 3 is shorter bythe ori-fla as compared to the case in which the ori-fla is not presentbetween the pushing pins 907 and 909. As described before, the pusheddistance can be changed by adjusting the size or the rotation angle ofthe disk-shaped cam 903.

If the wafers 3, having notches instead of ori-flas, are stored in astate where the notches face the back-side opening 8, when the waferpushing mechanism 9 is driven, the pushing pin 910 is brought intocontact with the wafer 3, releases the engagement of the wafer 3 andpushes the wafer to the position of the wafer 3″ represented by the twodot-chain line. In this case, the pushed distance of the wafer 3 issubstantially the same as that in the case where the ori-fla is notpresent between the pushing pins 907 and 909. The pushed distance canalso be changed in the same manner as described above. Further, sincethe pin 910 is much greater than the width of the notch, the amount of apush is constant regardless of whether there is a notch.

With the wafer transfer apparatus described above, even if the ori-flasof the wafers 3 are aligned toward the direction of the back-sideopening 8 or the wafer 3 has a notch, the same effect as that of thefirst embodiment is obtained. In addition, since a pin suffices, theapparatus can be more simplified and more advantageous in cost ascompared to the first embodiment.

The second embodiment can be modified in the same manner as in the firstembodiment. More specifically, although the structure for pressing outone by one the wafers 3 stored in the wafer cassette 4 has beendescribed as an example, the structure may simultaneously push out aplurality or all of the wafers. Further, it is possible to employ astructure for releasing the engagement and transferring each wafer 3 bymoving the pushing mechanism 9 and the transfer arm 5 up and down,instead of moving the cassette base 2 up and down.

Third Embodiment

In the structures of the first and second embodiments, the engagementbetween the circumferential edge portion of the wafer 3 and theback-around portions 701 can be released by driving the wafer pushingmechanism 9 by the motor 902.

In contrast, the third embodiment has a structure in which theengagement between the circumferential edge portion of the wafer 3 andthe back-around portions 701 is released by manually driving the pushingmechanism. A wafer transfer apparatus having such a pushing mechanism,more simplified and advantageous in cost, will be described below.

FIGS. 6 and 7 are schematic diagrams showing a wafer transfer apparatusaccording to the third embodiment. FIG. 6 is a cross sectional viewsimilar to FIG. 1. FIG. 7 is a view of a wafer cassette 4 viewed fromthe side of a back-side opening 8. The same elements as those shown inFIG. 1 are identified by the same reference numerals as those used inFIG. 1, and detailed descriptions thereof will be omitted.

A general structure will be described first.

In FIGS. 6 and 7, a wafer pushing mechanism 10 faces the back-sideopening 8 of the wafer cassette 4. The wafer pushing mechanism 9comprises a base 1001 and a column 1002 mounted upright on the base1001. A sub-bases 1004 is attached to upper and lower portions of thecolumn 1002 via linear guides 1003.

A handle 1007 is attached to the sub-base 1004. The sub-base 1004 can bemoved forward and backward relative to the back-side opening 8, alongthe direction of the linear guide 1003, by means of the handle 1007. Thestroke of the sub-base 1004 moved manually is set to a length enough tosurely release the engagement and push out the wafer 3 stored in thewafer cassette 4, in whatever direction the ori-fla of the wafer 3faces.

A spring 1006 is interposed between the sub-base 1004 and the column1002. Owing to the elastic force of the spring 1006, the sub-base 1004is always returned to a standby position separated from the back-sideopening 8.

In the front side of the sub-base 1004, facing the back-side opening 8,a plurality of wafer pushing pins 1005 are provided at positionscorresponding to all the wafers stored in the wafer cassette 47, so thatthey can be pushed out.

The wafer cassette 4 is mounted on the cassette base 2. The operatorpushes the handle 1007 to move the sub-base 1004 forward toward theback-side opening 8 against the elastic force of the spring 1006. By theforward movement, the wafer pushing pins 1005 attached to the sub-base1004 are brought into contact with the circumferential edge portions ofthe wafers 3, and push the wafers to release the engagement.

When the pushing operation of the handle 1007 is released in this state,the sub-base 1004 is returned to the standby position separated from theback-side opening 8 of the cassette 4 by the elastic force of the spring1006.

With the structure described above, since the wafer pushing mechanism 10is driven by manual means, the overall structure of the wafer pushingmechanism 10 can be simplified and advantageous in cost. Further, sinceall the wafers 3 in the wafer cassette 4 can be released from theengagement by one pushing operation, the cycle time can be shortened.

The present invention is not limited to the third embodiment describedabove, but can be modified variously, for example, as described below.

In the third embodiment, the contact portion between the pushing pin1005 and the wafer 3 may be rotatable in the same manner as in the caseof pushing pin of the first and second embodiments.

With this structure also, the wafer can be pushed out, while thecircumferential edge portion of the wafer 3 is prevented from engagingwith the pushing pin 1005.

Industrial Applicability

As described in the first to third embodiments, the wafer is pushed outby the wafer pushing mechanism, thereby preventing the engagementbetween the circumferential edge portion of the wafer and theback-around portions of the slot groove. As a result, when the wafer istaken out from the wafer cassette, damage of the wafer or an attractionerror of the transfer arm can be surely prevented, and wafers can besmoothly moved from one wafer cassette to another. Further, a transferprocess can be performed even by a transport wafer cassette which has anarrow pitch width.

What is claimed is:
 1. A wafer transfer apparatus for taking out a waferfrom a groove of a wafer cassette by moving a wafer taking out armrelative to the wafer cassette, the wafer transfer apparatus comprising:three rotatable pushing members; wafer pushing out means for bringing atleast two of said pushing members into contact with the wafer to betaken out at a rear end portion of the wafer cassette, and pushing outthe wafer, thereby releasing engagement between the wafer and the grooveof the wafer cassette; and transfer means for: (i) inserting the wafertaking out arm into the wafer cassette after releasing the engagementbetween the wafer and the groove of the wafer cassette, (ii) attractingthe wafer to the arm, and (iii) taking out the wafer from the cassette.2. The wafer transfer apparatus according to claim 1, wherein thepushing out means does not bring one of said pushing members intocontact with the wafer.
 3. The wafer transfer apparatus according toclaim 1, wherein each of the pushing members is rotatable by a bearingstructure.
 4. The wafer transfer apparatus according to claim 1, whereinthe wafer pushing out means comprises driving means for driving thepushing members linearly toward the wafer cassette.
 5. The wafertransfer apparatus according to claim 4, wherein the wafer pushing outmeans operates the pushing members to simultaneously push out aplurality of wafers.
 6. A wafer transfer apparatus for taking out awafer from a wafer cassette by moving a wafer taking out arm relative tothe wafer cassette, wherein the wafer cassette has grooves on both leftand right sides thereof for holding circumferential edges of a pluralityof wafers and an interval between the right and left grooves at a rearend part of the wafer cassette is narrower than an interval between theright and left grooves at a front end part of the wafer cassette, thewafer transfer apparatus comprising: three rollers rotatable about anaxis perpendicular to a surface of the wafer to be taken out; pushingout means for pushing out the wafer by bringing at least two of therollers into contact with the wafer at the rear end part of the wafercassette; and transfer means for: (i) inserting the wafer taking out arminto the wafer cassette after the wafer is pushed, (ii) placing thewafer on the arm, (iii) attracting the wafer, and (iv) taking the waferout from the cassette.
 7. The wafer transfer apparatus according toclaim 6, wherein two of the rollers are arranged at an interval widerthan a width of an orientation-flat of the wafer.
 8. The wafer transferapparatus according to claim 6, wherein the pushing out means comprises:a sub-base on which the pushing out member is mounted; a base forholding the sub-base via a linear movement guide; a spring for forcingthe sub-base in a direction toward the base; and a motor-driveneccentric cam for separating the sub-base from the base against springforce and linearly moving the sub-base toward a side of the wafercassette.
 9. The wafer transfer apparatus according to claim 6, whereinthe rollers have a length sufficient to push out one wafer.
 10. Thewafer transfer apparatus according to claim 6, wherein the rollers havea length sufficient to simultaneously push out a plurality of wafers.11. The wafer transfer apparatus according to claim 6, wherein therollers have a length sufficient to simultaneously push out all wafersin the wafer cassette.
 12. A wafer apparatus for taking out a wafer froma wafer cassette by moving a wafer taking out arm relative to the wafercassette, wherein the wafer cassette has grooves on both left and rightsides thereof for holding circumferential edges of a plurality of wafersand an interval between the right and left grooves at a rear end part ofthe wafer cassette is narrower than an interval between the right andleft grooves at a front end part of the wafer cassette, the wafertransfer apparatus comprising: three rotatable pushing members; waferpushing out means for bringing at least two of said pushing members intocontact with the wafer to be taken out at a rear end portion of thewafer cassette, and pushing out the wafer, thereby releasing engagementbetween the wafer and the right and left grooves of the wafer cassette;and transfer means for: (i) inserting the wafer taking out arm into thewafer cassette after pushing out the wafer, (ii) placing the wafer onthe arm, (iii) attracting the wafer, and (iv) taking out the wafer fromthe cassette.
 13. The wafer transfer apparatus according to claim 12,wherein two of the pushing members are arranged at an interval widerthan a width of an orientation-flat of the wafer to be taken out. 14.The wafer transfer apparatus according to claim 12, wherein the pushingout means comprises: a sub-base on which the pushing out member ismounted; a base for holding the sub-base via a linear movement guide; aspring for forcing the sub-base in a direction toward the base; and amotor-driven eccentric cam for separating the sub-base from the baseagainst spring force and linearly moving the sub-base toward a side ofthe wafer cassette.
 15. The wafer transfer apparatus according to claim12, wherein a length of each of the pushing members is substantiallyequal to a length of an opening of the cassette in a direction ofstacking of the plurality of wafers.
 16. A wafer transfer apparatus fortaking out a wafer from a wafer cassette by moving a wafer taking outarm relative to the wafer cassette, wherein the wafer cassette hasgrooves on both left and right sides thereof for holding circumferentialedges of a plurality of wafers and an interval between the right andleft grooves at a rear end part of the wafer cassette is narrower thanan interval between the right and left grooves at a front end part ofthe wafer cassette, the wafer transfer apparatus comprising: a pushingmember comprising at least one roller rotatable about an axisperpendicular to a surface of the wafer to be taken out; pushing outmeans for pushing out the wafer by bringing the pushing member intocontact with the wafer at the rear end part of the wafer cassette; andtransfer means for: (i) inserting the wafer taking out arm into thewafer cassette after the wafer is pushed, (ii) placing the wafer on thearm, (iii) attracting the wafer, and (iv) taking the wafer out from thecassette; wherein the pushing out means comprises: a sub-base on whichthe pushing member is mounted; a base for holding the sub-base via alinear movement guide; a spring for forcing the sub-base in a directiontoward the base; and a motor-driven eccentric cam for separating thesub-base from the base against spring force and linearly moving thesub-base toward a side of the wafer cassette.
 17. A wafer apparatus fortaking out a wafer from a wafer cassette by moving a wafer taking outarm relative to the wafer cassette, wherein the wafer cassette hasgrooves on both left and right sides thereof for holding circumferentialedges of a plurality of wafers and an interval between the right andleft grooves at a rear end part of the wafer cassette is narrower thanan interval between the right and left grooves at a front end part ofthe wafer cassette, the wafer transfer apparatus comprising: threerotatable pushing members; wafer pushing out means for bringing at leasttwo of said pushing members into contact with the wafer to be taken outat a rear end portion of the wafer cassette, and pushing out the wafer,thereby releasing engagement between the wafer and the right and leftgrooves of the wafer cassette; and transfer means for: (i) inserting thewafer taking out arm into the wafer cassette after pushing out thewafer, (ii) placing the wafer on the arm, (iii) attracting the wafer,and (iv) taking out the wafer from the cassette; wherein the pushing outmeans comprises: a sub-base on which the pushing members is mounted; abase for holding the sub-base via a linear movement guide; a spring forforcing the sub-base in a direction toward the base; and a motor-driveneccentric cam for separating the sub-base from the base against springforce and linearly moving the sub-base toward a side of the wafercassette.